What is the MLB record for the most walks (bases on balls) allowed in a single game (9 inning game) by a pitcher who ultimately still recorded the win?
The answer is 13. It has happened twice, once in a 10 inning game, and once in a 9 inning game.
The nine inning game was
The Reds beat the Phillies 10-9 in regulation. Schneider was charged with 6 runs, all in the 9th failing to record an out. The reliever that followed him also failed to record and out. Fred Toney was finally able to come in and get the save. No play by play is available so the exact order of events is unknown.
What is for sure is that Schneider did give up 13 walks and still managed to take home the victory.
Retrosheet also has the box score here
In this game, Lefty Gomez gave up 11 walks and got the win (in a shutout, no less.) As viewable here, there have been three 9-inning games in which 16 walks were given up,
but I can't find the box scores to those particular games. but all of those were losses. Looking at those pitchers directly, we can see that Bruno Haas didn't get the win as he has no career wins.
Bill George pitched in 13 games that year and gave up 89 walks, 22 wild pitches and 14 hit batters. I have no idea how he got the 3 wins that he did.
George Van Haltren had a pretty decent record that year, but again, I can't find box scores, so I don't know if he recorded the win or not.
There are a couple of games where 13 walks were given up, but those were in extra innings, so I excluded those from my search.